Polyamide nanofiber nonwovens

ABSTRACT

A nanofiber nonwoven product is disclosed which comprises a polyamide with a relative viscosity from 2 to 330, spun into nanofibers with an average diameter of less than 1000 nanometers (1 micron). In general, the inventive products are prepared by: (a) providing a polyamide composition, wherein the polyamide has a relative viscosity from 2 to 330; (b) melt spinning the polyamide composition into a plurality of nanofibers having an average fiber diameter of less than 1 micron, followed by (c) forming the nanofibers into the product.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 16/003,528, filed onJun. 8, 2018, which claims priority to U.S. provisional patentapplication Nos. 62/516,867, filed Jun. 8, 2017, and 62/518,769, filedJun. 13, 2017, which are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

The present disclosure relates to polyamide nanofiber nonwovens that maybe useful for air and liquid filtration, breathable fabrics for apparel,acoustics, composites and packaging, as well as other applications.

BACKGROUND

Polymer membranes, including nanofiber and microfiber nonwovens areknown in the art and are used for a variety of purposes, including inconnection with filtration media and apparel. Known techniques forforming finely porous polymer structures include xerogel and aerogelmembrane formation, electrospinning, melt-blowing, as well ascentrifugal-spinning with a rotating spinneret, and two-phase polymerextrusion through a thin channel using a propellant gas. Thesetechniques are either expensive or do not form nanofibers, e.g.,polyamide nanofibers, with acceptable fiber diameter distributions.Electrospinning, in particular, is a relatively expensive process, andcurrent melt-blowing techniques, while less expensive, are unable attainthe nanofiber size that electrospinning can attain.

As one example, US Pub. No. 2014/0097558 A1 relates generally to methodsof manufacture of a filtration media, such as a personal protectionequipment mask or respirator, which incorporates an electrospinningprocess to form nanofibers onto a convex mold, which may, for example,be in the shape of a human face. US Pub. No. 2015/0145175 A1 providessimilar disclosure.

WO 2014/074818 A2 discloses nanofibrous meshes and xerogels used forselectively filtering target compounds or elements from a liquid. Alsodescribed are methods for forming nanofibrous meshes and xerogels,methods for treating a liquid using nanofibrous meshes and xerogels, andmethods for analyzing a target compound or element using nanofibrousmeshes and xerogels. The nanofibers are comprised of polysiloxanes.

WO 2015/003170 A2 relates to nonwoven textiles consisting of webs ofsuperfine fibers, e.g., fibers with diameters in nanoscale or micronscale ranges, for use in articles that have, for example a predetermineddegree of waterproofness with breathability, or windproofness withbreathability. The fibers may comprise polyurethane-based material orpolytetrafluoroethylene.

WO 2015/153477 A1 relates to a fiber construct suitable for use as afill material for insulation or padding, comprising: a primary fiberstructure comprising a predetermined length of fiber; a secondary fiberstructure, the secondary fiber structure comprising a plurality ofrelatively short loops spaced along a length of the primary fiber. Amongthe techniques enumerated for forming the fiber structures includeelectrospinning, melt-blowing, melt-spinning and centrifugal-spinning.The products are reported to mimic goose-down, with fill power in therange of 550 to 900.

Despite the variety of techniques and materials proposed, conventionalproducts have much to be desired in terms of manufacturing costs,processability, and product properties.

SUMMARY

In some embodiments, the present disclosure is directed to a nanofibernonwoven product comprising polyamide nanofibers, wherein the producthas a relative viscosity from 2 to 330, and wherein the nanofibers havean average diameter from 100 to 1000 nanometers. The melt point of theproduct may be 225° C. or greater. In some aspects, no more than 20% ofthe nanofibers have a diameter of greater than 700 nanometers. Thepolyamide may comprise nylon 66 or nylon 6/66. In some aspects, thepolyamide is a high temperature nylon. In some aspects, the polyamidecomprises N6, N66, N6T/66, N612, N6/66, N6I/66, N66/6I/6T, N11, and/orN12, wherein “N” means Nylon. The product may have an Air PermeabilityValue of less than 600 CFM/ft². The product may have a basis weight of150 GSM or less. The product may have a basis weight of 150 GSM or less.The product may have a TDI of at least 20 ppm. The product may have anODI of at least 1 ppm. In some aspects, the product is free of solvent.In other aspects, the product comprises less than 5000 ppm solvent.

In some embodiments, the present disclosure is directed to a nanofibernonwoven product comprising a polyamide which is spun into nanofiberswith an average diameter from 100 to 1000 nanometers and formed intosaid nonwoven product, wherein the polyamide has a relative viscosityfrom 2 to 330. The melt point of the product may be 225° C. or greater.In some aspects, no more than 20% of the nanofibers have a diameter ofgreater than 700 nanometers. The polyamide may comprise nylon 66 ornylon 6/66. In some aspects, the polyamide is a high temperature nylon.In some aspects, the polyamide comprises N6, N66, N6T/66, N612, N6/66,N6I/66, N66/6I/6T, N11, and/or N12, wherein “N” means Nylon. The productmay have an Air Permeability Value of less than 600 CFM/ft². The productmay have a basis weight of 150 GSM or less. The product may have a basisweight of 150 GSM or less. The product may have a TDI of at least 20ppm. The product may have an ODI of at least 1 ppm. In some aspects, theproduct is free of solvent. In other aspects, the product comprises lessthan 5000 ppm solvent.

In some embodiments, the present disclosure is directed to a nanofibernonwoven product comprising a nylon 66 polyamide which is melt spun intonanofibers and formed into said nonwoven product, wherein the producthas a TDI of at least 20 ppm and an ODI of at least 1 ppm. The productmay have an Air Permeability Value of less than 600 CFM/ft². The productmay have a basis weight of 150 GSM or less. In some aspects, the productis free of solvent. In other aspect, the product comprises less than5000 ppm solvent. In some aspects, no more than 20% of the nanofibershave a diameter of greater than 700 nanometers. The nylon 66 polyamidemay have an RV from 2 to 330. The product may have an RV from 2 to 330.

In some embodiments, the present disclosure is directed to a nanofibernonwoven product comprising a nylon 66 polyamide which is melt spun intonanofibers and formed into said nonwoven product, wherein no more than20% of the nanofibers have a diameter of greater than 700 nanometers.The product may have an Air Permeability Value of less than 600 CFM/ft².The product may have a basis weight of 150 GSM or less. The product mayhave a basis weight of 150 GSM or less. The product may have a TDI of atleast 20 ppm. The product may have an ODI of at least 1 ppm. In someaspects, the product is free of solvent. In other aspects, the productcomprises less than 5000 ppm solvent. The nylon 66 polyamide may have anRV from 2 to 330. The product may have an RV from 2 to 330.

In some embodiments, the present disclosure is directed to a method ofmaking a nanofiber nonwoven product, the method comprising: (a)providing a polyamide composition, wherein the polyamide has a relativeviscosity from 2 to 330; (b) spinning the polyamide composition into aplurality of nanofibers having an average fiber diameter from 100 to1000 nanometers; and (c) forming the nanofibers into the nanofibernonwoven product, wherein the polyamide nanofiber layer has an averagenanofiber diameter from 100 to 1000 nanometers and a relative viscosityfrom 2 to 330. In some aspects, the polyamide composition is melt spunby way of melt-blowing through a die into a high velocity gaseousstream. In some aspects, the polyamide composition is melt-spun by2-phase propellant-gas spinning, including extruding the polyamidecomposition in liquid form with pressurized gas through a fiber-formingchannel. The product may be formed by collecting the nanofibers on amoving belt. The polyamide nanofiber layer may have a basis weight of150 GSM or less. In some aspects, the relative viscosity of thepolyamide in the nanofiber nonwoven product is reduced as compared tothe polyamide composition prior to spinning and forming the product. Insome aspects, the relative viscosity of the polyamide in the nanofibernonwoven product is the same or increased as compared to the polyamidecomposition prior to spinning and forming the product.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure is described in detail below with reference to thedrawings wherein like numerals designate similar parts and wherein:

FIG. 1 and FIG. 2 are separate schematic diagrams of a 2-phasepropellant-gas spinning system useful in connection with the presentdisclosure;

FIG. 3 is a photomicrograph of a nanofiber nylon 66 melt spun into anonwoven having an RV of 7.3 at a magnification of 50×; and

FIG. 4 is a photomicrograph of a nanofiber of a grade from FIG. 3 ofnylon 66 melt spun into a nonwoven having an RV of 7.3 at amagnification of 8000×; and

FIG. 5 is a schematic diagram of a melt blowing process in connectionwith embodiments of the present disclosure.

FIG. 6 is a photomicrograph of a nanofiber of nylon 66 with an RV of 36at a magnification of 100×.

FIG. 7 is a graph comparing thermal degradation index and oxidativedegradation index values for nanofiber samples as a function of dietemperature.

FIG. 8 is a graph comparing thermal degradation index and oxidativedegradation index values for nanofiber samples as a function of meterpump speed.

DETAILED DESCRIPTION

Overview

The present disclosure is directed, in part, to a nanofiber nonwovenproduct formed from a (precursor) polyamide composition. The product mayhave a Relative Viscosity (RV) from 2 to 330, e.g., from 2 to 300, from2 to 275, from 2 to 250, from 2 to 225, from 2 to 200, 2 to 100, from 2to 60, from 2 to 50, from 2 to 40, from 10 to 40, or from 15 to 40(additional RV ranges and limits are provided herein). The polyamidecomposition may be spun or melt blown into fibers, e.g., nanofibers. Thepolyamide nanofibers may have an average diameter of less than 1000nanometers (1 micron) and may be formed into the nonwoven product.Traditional melt spinning/melt blowing techniques have been unable toform fibers having low average diameters, e.g., nanofibers. Typical meltspun/melt blown fiber average diameters are at least 1 micron and cannotachieve the surface area to volume ratio that a nanofiber can achieve.Such an increased surface area to volume ratio is beneficial in manyapplications.

The inventors have found that by utilizing a particular precursorpolyamide having specific characteristics in a particular (melt)spinning process, nonwoven nanofibers having synergistic features areformed. Without being bound by theory, it is postulated that the use ofa polyamide composition having an RV of 330 or less leads to fibershaving small diameters, previously unachievable by conventionalsolvent-free processes. As an additional benefit, the production rate isadvantageously improved, for example, on a per meter basis, overprocesses such as electrospinning and solution spinning. Suchimprovements may be by at least 5%, e.g., by at least 10%, by at least15%, by at least 20%, by at least 25%, or by at least 30%.

Also, the inventors have found that the disclosed processes, techniques,and/or precursors, yield nanofibers having reduced oxidative degradationand thermal degradation indices as compared to nonwoven productsprepared from other precursors and by other processes. Theseimprovements advantageously result in products with improved durability.

Additionally, the process may be conducted in the absence of solvents,e.g., does not use solvents, such as formic acid and others describedherein, which reduces environmental concerns with disposing of thesolvents and handling of the solvents during preparation of thesolutions. Such solvents are used in solution spinning and the solutionspinning process therefore requires additional capital investment todispose of the solvents. Additional costs may be incurred due to theneed for a separate solvent room and a scrubber area. There are alsohealth risks associated with some solvents. Accordingly, the nanofibernonwoven product may be free of residual solvents, e.g., as arenecessarily present in solution spun products. For example, residualsolvent from 2.2 to 5 wt. % may be found in solution spun processes, asdisclosed by L. M. Guerrini, M. C. Branciforti, T Canova, and R. E. S.Bretas, Materials Research, Vol. 12, No. 2, pp 181-190 (2009).

In some aspects, no adhesives are included in the nanofiber nonwovenproduct. Such adhesives are often included to adhere electrospun fibersto scrims. Although the nanofiber nonwoven product described herein maybe blown onto a scrim, no such adhesives are necessary.

In some embodiments, the nanofiber nonwoven product is produced by: (a)providing a (spinnable) polyamide composition, wherein the polyamidecomposition has the RV discussed herein; (b) spinning the polyamidecomposition into a plurality of nanofibers having an average fiberdiameter of less than 1 micron, e.g., by way of a process directed to2-phase propellant-gas spinning, including extruding the polyamidecomposition in liquid form with pressurized gas through a fiber-formingchannel, and (c) forming the nanofibers into the nanofiber nonwovenproduct. The general process is illustrated in FIGS. 1 and 2.

Particularly preferred polyamides include nylon 66, as well ascopolymers, blends, and alloys of nylon 66 with nylon 6. Otherembodiments include nylon derivatives, copolymers, terpolymers, blendsand alloys containing or prepared from nylon 66 or nylon 6, copolymersor terpolymers with the repeat units noted above including but notlimited to: N6T/66, N612, N6/66, N6I/66, N11, and N12, wherein “N” meansNylon. Another preferred embodiment includes High Temperature Nylons(“HTN”) as well as blends, derivatives, copolymers or terpolymerscontaining them. Furthermore, another preferred embodiment includes longchain aliphatic polyamide made with long chain diacids as well asblends, derivatives or copolymers containing them.

FIG. 1 illustrates an exemplary technique wherein a 2 phase propellantgas spinning process may be used for making the nanofiber. FIG. 2illustrates a general melt blowing technique.

In particular, disclosed herein is an embodiment wherein a method ofmaking a nanofiber nonwoven product wherein the nonwoven fabric ismelt-spun by way of melt-blowing through a spinneret into a highvelocity gaseous stream. More particularly, in one embodiment, thenonwoven fabric is melt-spun by 2-phase propellant-gas spinning,including extruding the polyamide composition in liquid form withpressurized gas through a fiber-forming channel.

Definitions and Test Methods

Terminology used herein is given its ordinary meaning consistent withthe definitions set forth below.

Spinning, as used herein, refers to the steps of melting a polyamidecomposition and forming the polyamide composition into fibers. Examplesof spinning include centrifugal spinning, melt blowing, spinning througha spinneret (e.g., a spinneret without a charge) or die, and“island-in-the sea” geometry.

GSM refers to basis weight in grams per square meter (g/m²), RV refersto Relative Viscosity.

Percentages and parts per million (ppm) refer to weight percent or partsper million by weight based on the weight of the respective compositionunless otherwise indicated.

Some typical definitions and test methods are further recited in US Pub.Nos. 2015/0107457 and 2015/0111019, which are incorporated herein byreference. The term “nanofiber nonwoven product” for example, refers toa web of a multitude of essentially randomly oriented nanofibers whereno overall repeating structure can be discerned by the naked eye in thearrangement of nanofibers. The nanofibers can be bonded to each otherand/or entangled to impart strength and integrity to the web. In somecases the nanofibers are not bonded to one another and may or may not beentangled. The nanofibers can be staple nanofibers or continuousnanofibers, and can comprise a single material or a multitude ofmaterials, either as a combination of different nanofibers or as acombination of similar nanofibers each comprising of differentmaterials. The nanofiber nonwoven product is constructed predominantlyof nanofibers. “Predominantly” means that greater than 50% of the fibersin the web are nanofibers. The term “nanofiber” refers to fibers havinga number average diameter less than 1000 nm (1 micron). In the case ofnonround cross-sectional nanofibers, the term “diameter” as used hereinrefers to the greatest cross-sectional dimension.

To the extent not indicated otherwise, test methods for determiningaverage fiber diameters, are as indicated in Hassan et al., J 20Membrane Sci., 427, 336-344, 2013, unless otherwise specified.

Basis Weight may be determined by ASTM D-3776 and reported in GSM(g/m²).

“Consisting essentially of” refers to the recited components andexcludes other ingredients which would substantially change the basicand novel characteristics of the composition or article. Unlessotherwise indicated or readily apparent, a composition or articleconsists essentially of the recited or listed components when thecomposition or article includes 90% or more by weight of the recited orlisted components. That is, the terminology excludes more than 10%unrecited components.

Air permeability is measured using an Air Permeability Tester, availablefrom Precision Instrument Company, Hagerstown, Md. Air permeability isdefined as the flow rate of air at 23±1° C. through a sheet of materialunder a specified pressure head. It is usually expressed as cubic feetper minute per square foot at 0.50 in. (12.7 mm) water pressure, in cm³per second per square cm or in units of elapsed time for a given volumeper unit area of sheet. The instrument referred to above is capable ofmeasuring permeability from 0 to approximately 5000 cubic feet perminute per square foot of test area. For purposes of comparingpermeability, it is convenient to express values normalized to 5 GSMbasis weight. This is done by measuring Air Permeability Value and basisweight of a sample (@ 0.5″ H2O typically), then multiplying the actualAir Permeability Value by the ratio of actual basis weight in GSM to 5.For example, if a sample of 15 GSM basis weight has a Value of 10CFM/ft², its Normalized 5 GSM Air Permeability Value is 30 CFM/ft².

Polyamide

As used herein, polyamide composition and like terminology refers tocompositions containing polyamides including copolymers, terpolymers,polymer blends, alloys and derivatives of polyamides. Further, as usedherein, a “polyamide” refers to a polymer, having as a component, apolymer with the linkage of an amino group of one molecule and acarboxylic acid group of another molecule. In some aspects, thepolyamide is the component present in the greatest amount. For example,a polyamide containing 40 wt. % nylon 6, 30 wt. % polyethylene, and 30wt. % polypropylene is referred to herein as a polyamide since the nylon6 component is present in the greatest amount. Additionally, a polyamidecontaining 20 wt. % nylon 6, 20 wt. % nylon 66, 30 wt. % polyethylene,and 30 wt. % polypropylene is also referred to herein as a polyamidesince the nylon 6 and nylon 66 components, in total are the componentspresent in the greatest amount.

Exemplary polyamides and polyamide compositions are described inKirk-Othmer, Encyclopedia of Chemical Technology, Vol. 18, pp. 328-371(Wiley 1982), the disclosure of which is incorporated by reference.

Briefly, polyamides are generally known as compounds that containrecurring amide groups as integral parts of the main polymer chains.Linear polyamides are of particular interest and may be formed fromcondensation of bifunctional monomers. Polyamides are frequentlyreferred to as nylons. Although they generally are considered ascondensation polymers, polyamides also are formed by additionpolymerization. This method of preparation is especially important forsome polymers in which the monomers are cyclic lactams, e.g., Nylon 6.Particular polymers and copolymers and their preparation are seen in thefollowing patents: U.S. Pat. Nos. 4,760,129; 5,504,185; 5,543,495;5,698,658; 6,011,134; 6,136,947; 6,169,162; 7,138,482; 7,381,788; and8,759,475.

There are numerous advantages of using polyamides, specifically nylons,in commercial applications. Nylons are generally chemical andtemperature resistant, resulting in superior performance to otherparticles. They are also known to have improved strength, elongation,and abrasion resistance as compared to other polymers. Nylons are alsovery versatile, allowing for their use in a variety of applications.

A class of polyamides particularly preferred for some applicationsincludes High Temperature Nylons (HTN's) as are described in Glasscocket al., High Performance Polyamides Fulfill Demanding Requirements forAutomotive Thermal Management Components, (DuPont),http://www2.dupont.com/Automotive/en US/assets/downloads/knowledg e%20center/HTN-whitepaper-R8.pdf available online Jun. 10, 2016. Suchpolyamides typically include one or more of the structures seen in thefollowing:

Non-limiting examples of polymers included in the polyamides includepolyamides, polypropylene and copolymers, polyethylene and copolymers,polyesters, polystyrenes, polyurethanes, and combinations thereof.Thermoplastic polymers and biodegradable polymers are also suitable formelt blowing or melt spinning into nanofibers of the present disclosure.As discussed herein, the polymers may be melt spun or melt blown, with apreference for melt spinning or melt blowing by 2-phase propellant-gasspinning, including extruding the polyamide composition in liquid formwith pressurized gas through a fiber-forming channel.

Melt points of nylon nanofiber products described herein, includingcopolymers and terpolymers, may be between 223° C. and 390° C., e.g.,from 223 to 380, or from 225° C. to 350° C. Additionally, the melt pointmay be greater than that of conventional nylon 66 melt points dependingon any additional polymer materials that are added.

Other polymer materials that can be used in the polyamide nanofibernonwovens of the disclosure include both addition polymer andcondensation polymer materials such as polyolefin, polyacetal, polyamide(as previously discussed), polyester, cellulose ether and ester,polyalkylene sulfide, polyarylene oxide, polysulfone, modifiedpolysulfone polymers and mixtures thereof. Preferred materials that fallwithin these generic classes include polyamides, polyethylene,polybutylene terephthalate (PBT), polypropylene, poly(vinylchloride),polymethylmethacrylate (and other acrylic resins), polystyrene, andcopolymers thereof (including ABA type block copolymers),poly(vinylidene fluoride), poly(vinylidene chloride), polyvinylalcoholin various degrees of hydrolysis (87% to 99.5%) in crosslinked andnon-crosslinked forms. Addition polymers tend to be glassy (a Tg greaterthan room temperature). This is the case for polyvinylchloride andpolymethylmethacrylate, polystyrene polymer compositions or alloys orlow in crystallinity for polyvinylidene fluoride and polyvinylalcoholmaterials. Nylon copolymers embodied herein, can be made by combiningvarious diamine compounds, various diacid compounds and various cycliclactam structures in a reaction mixture and then forming the nylon withrandomly positioned monomeric materials in a polyamide structure. Forexample, a nylon 66-6,10 material is a nylon manufactured fromhexamethylene diamine and a C6 and a C10 blend of diacids. A nylon6-66-6,10 is a nylon manufactured by copolymerization ofepsilonaminocaproic acid, hexamethylene diamine and a blend of a C6 anda C10 diacid material.

In some embodiments, such as that described in U.S. Pat. No. 5,913,993,a small amount of polyethylene polymer can be blended with a nyloncompound used to form a nanofiber nonwoven fabric with desirablecharacteristics. The addition of polyethylene to nylon enhances specificproperties such as softness. The use of polyethylene also lowers cost ofproduction, and eases further downstream processing such as bonding toother fabrics or itself. The improved fabric can be made by adding asmall amount of polyethylene to the nylon feed material used inproducing a nanofiber melt blown fabric. More specifically, the fabriccan be produced by forming a blend of polyethylene and nylon 66,extruding the blend in the form of a plurality of continuous filaments,directing the filaments through a die to melt blow the filaments,depositing the filaments onto a collection surface such that a web isformed.

The polyethylene useful in the process of this embodiment of the subjectdisclosure preferably may have a melt index between about 5 grams/10 minand about 200 grams/10 min and, e.g., between about 17 grams/10 min andabout 150 grams/10 min. The polyethylene should preferably have adensity between about 0.85 grams/cc and about 1.1 grams/cc and, e.g.,between about 0.93 grams/cc and about 0.95 grams/cc. Most preferably,the melt index of the polyethylene is about 150 and the density is about0.93.

The polyethylene used in the process of this embodiment of the subjectdisclosure can be added at a concentration of about 0.05% to about 20%.In a preferred embodiment, the concentration of polyethylene will bebetween about 0.1% and about 1.2%. Most preferably, the polyethylenewill be present at about 0.5%. The concentration of polyethylene in thefabric produced according to the method described will be approximatelyequal to the percentage of polyethylene added during the manufacturingprocess. Thus, the percentage of polyethylene in the fabrics of thisembodiment of the subject disclosure will typically range from about0.05% to about 20% and will preferably be about 0.5%. Therefore, thefabric will typically comprise between about 80 and about 99.95 percentby weight of nylon. The filament extrusion step can be carried outbetween about 250° C. and about 325° C. Preferably, the temperaturerange is about 280° C. to about 315° C. but may be lower if nylon 6 isused.

The blend or copolymer of polyethylene and nylon can be formed in anysuitable manner. Typically, the nylon compound will be nylon 66;however, other polyamides of the nylon family can be used. Also,mixtures of nylons can be used. In one specific example, polyethylene isblended with a mixture of nylon 6 and nylon 66. The polyethylene andnylon polymers are typically supplied in the form of pellets, chips,flakes, and the like. The desired amount of the polyethylene pellets orchips can be blended with the nylon pellets or chips in a suitablemixing device such as a rotary drum tumbler or the like, and theresulting blend can be introduced into the feed hopper of theconventional extruder or the melt blowing line. The blend or copolymercan also be produced by introducing the appropriate mixture into acontinuous polymerization spinning system.

Further, differing species of a general polymeric genus can be blended.For example, a high molecular weight styrene material can be blendedwith a low molecular weight, high impact polystyrene. A Nylon-6 materialcan be blended with a nylon copolymer such as a Nylon-6; 66; 6,10copolymer. Further, a polyvinylalcohol having a low degree of hydrolysissuch as a 87% hydrolyzed polyvinylalcohol can be blended with a fully orsuperhydrolyzed polyvinylalcohol having a degree of hydrolysis between98 and 99.9% and higher. All of these materials in admixture can becrosslinked using appropriate crosslinking mechanisms. Nylons can becrosslinked using crosslinking agents that are reactive with thenitrogen atom in the amide linkage. Polyvinyl alcohol materials can becrosslinked using hydroxyl reactive materials such as monoaldehydes,such as formaldehyde, ureas, melamine-formaldehyde resin and itsanalogues, boric acids and other inorganic compounds, dialdehydes,diacids, urethanes, epoxies and other known crosslinking agents.Crosslinking technology is a well-known and understood phenomenon inwhich a crosslinking reagent reacts and forms covalent bonds betweenpolymer chains to substantially improve molecular weight, chemicalresistance, overall strength and resistance to mechanical degradation.

One preferred mode is a polyamide comprising a first polymer and asecond, but different polymer (differing in polymer type, molecularweight or physical property) that is conditioned or treated at elevatedtemperature. The polymer blend can be reacted and formed into a singlechemical specie or can be physically combined into a blended compositionby an annealing process. Annealing implies a physical change, likecrystallinity, stress relaxation or orientation. Preferred materials arechemically reacted into a single polymeric specie such that aDifferential Scanning calorimeter (DSC) analysis reveals a singlepolymeric material to yield improved stability when contacted with hightemperature, high humidity and difficult operating conditions. Preferredmaterials for use in the blended polymeric systems include nylon 6;nylon 66; nylon 6,10; nylon (6-66-6,10) copolymers and other lineargenerally aliphatic nylon compositions.

A suitable polyamide may include for example, 20% nylon 6, 60% nylon 66and 20% by weight of a polyester. The polyamide may include combinationsof miscible polymers or combinations of immiscible polymers.

In some aspects, the polyamide may include nylon 6. In terms of lowerlimits, the polyamide may include nylon 6 in an amount of at least 0.1wt. %, e.g., at least 1 wt. %, at least 5 wt. %, at least 10 wt. %, atleast 15 wt. %, or at least 20 wt. %. In terms of upper limits, thepolyamide may include nylon 6 in an amount of 99.9 wt. % or less, 99 wt.% or less, 95 wt. % or less, 90 wt. % or less, 85 wt. % or less, or 80wt. % or less. In terms of ranges, the polyamide may comprise nylon 6 inan amount from 0.1 to 99.9 wt. %, e.g., from 1 to 99 wt. %, from 5 to 95wt. %, from 10 to 90 wt. %, from 15 to 85 wt. %, or from 20 to 80 wt. %.

In some aspects, the polyamide may include nylon 66. In terms of lowerlimits, the polyamide may include nylon 66 in an amount of at least 0.1wt. %, e.g., at least 1 wt. %, at least 5 wt. %, at least 10 wt. %, atleast 15 wt. %, or at least 20 wt. %. In terms of upper limits, thepolyamide may include nylon 66 in an amount of 99.9 wt. % or less, 99wt. % or less, 95 wt. % or less, 90 wt. % or less, 85 wt. % or less, or80 wt. % or less. In terms of ranges, the polyamide may comprise nylon66 in an amount from 0.1 to 99.9 wt. %, e.g., from 1 to 99 wt. %, from 5to 95 wt. %, from 10 to 90 wt. %, from 15 to 85 wt. %, or from 20 to 80wt. %.

In some aspects, the polyamide may include nylon 61. In terms of lowerlimits, the polyamide may include nylon 61 in an amount of at least 0.1wt. %, e.g., at least 0.5 wt. %, at least 1 wt. %, at least 5 wt. %, atleast 7.5 wt. %, or at least 10 wt. %. In terms of upper limits, thepolyamide may include nylon 61 in an amount of 50 wt. % or less, 40 wt.% or less, 35 wt. % or less, 30 wt. % or less, 25 wt. % or less, or 20wt. % or less. In terms of ranges, the polyamide may comprise nylon 61in an amount from 0.1 to 50 wt. %, e.g., from 0.5 to 40 wt. %, from 1 to35 wt. %, from 5 to 30 wt. %, from 7.5 to 25 wt. %, or from 10 to 20 wt.%.

In some aspects, the polyamide may include nylon 6T. In terms of lowerlimits, the polyamide may include nylon 6T in an amount of at least 0.1wt. %, e.g., at least 1 wt. %, at least 5 wt. %, at least 10 wt. %, atleast 15 wt. %, or at least 20 wt. %. In terms of upper limits, thepolyamide may include nylon 6T in an amount of 50 wt. % or less, 47.5wt. % or less, 45 wt. % or less, 42.5 wt. % or less, 40 wt. % or less,or 37.5 wt. % or less. In terms of ranges, the polyamide may comprisenylon 6T in an amount from 0.1 to 50 wt. %, e.g., from 1 to 47.5 wt. %,from 5 to 45 wt. %, from 10 to 42.5 wt. %, from 15 to 40 wt. %, or from20 to 37.5 wt. %.

Block copolymers are also useful in the process of this disclosure. Withsuch copolymers the choice of solvent swelling agent is important. Theselected solvent is such that both blocks were soluble in the solvent.One example is an ABA (styrene-EP-styrene) or AB (styrene-EP) polymer inmethylene chloride solvent. If one component is not soluble in thesolvent, it will form a gel. Examples of such block copolymers areKraton® type of styrene-b-butadiene and styrene-b-hydrogenated butadiene(ethylene propylene), Pebax® type of e-caprolactam-b-ethylene oxide,Sympatex® polyester-b-ethylene oxide and polyurethanes of ethylene oxideand isocyanates.

Addition polymers like polyvinylidene fluoride, syndiotacticpolystyrene, copolymer of vinylidene fluoride and hexafluoropropylene,polyvinyl alcohol, polyvinyl acetate, amorphous addition polymers, suchas poly(acrylonitrile) and its copolymers with acrylic acid andmethacrylates, polystyrene, poly(vinyl chloride) and its variouscopolymers, poly(methyl methacrylate) and its various copolymers, areknown to be solution spun with relative ease because they are soluble atlow pressures and temperatures. It is envisioned these can be melt spunper the instant disclosure as one method of making nanofibers.

There is a substantial advantage to forming polymeric compositionscomprising two or more polymeric materials in polymer admixture, alloyformat or in a crosslinked chemically bonded structure. We believe suchpolymer compositions improve physical properties by changing polymerattributes such as improving polymer chain flexibility or chainmobility, increasing overall molecular weight and providingreinforcement through the formation of networks of polymeric materials.

In one embodiment of this concept, two related polymer materials can beblended for beneficial properties. For example, a high molecular weightpolyvinylchloride can be blended with a low molecular weightpolyvinylchloride. Similarly, a high molecular weight nylon material canbe blended with a low molecular weight nylon material.

RV of Polyamide and of Nanofiber Nonwoven Product

RV of polyamides (and resultant products) is generally a ratio ofsolution or solvent viscosities measured in a capillary viscometer at25° C. (ASTM D 789) (2015). For present purposes the solvent is formicacid containing 10% by weight water and 90% by weight formic acid. Thesolution is 8.4% by weight polymer dissolved in the solvent.

The RV (η_(r)) as used with respect to the disclosed polymers andproducts is the ratio of the absolute viscosity of the polymer solutionto that of the formic acid:η_(r)=(η_(p)/η_(f))=(f _(r) ×d _(p) ×t _(p))/η_(f)where: d_(p)=density of formic acid-polymer solution at 25° C.,t_(p)=average efflux time for formic acid-polymer solution,η_(f)=absolute viscosity of formic acid, kPa×s (E+6 cP) andf_(r)=viscometer tube factor, mm²/s (cSt)/s=η_(r)/t₃.

A typical calculation for a 50 RV specimen:ηr=(fr×dp×tp)/ηfwhere:

fr=viscometer tube factor, typically 0.485675 cSt/s

dp=density of the polymer—formic solution, typically 1.1900 g/ml

tp=average efflux time for polymer—formic solution, typically 135.00 s

ηf=absolute viscosity of formic acid, typically 1.56 cP

giving an RV of ηr=(0.485675 cSt/s×1.1900 g/ml×135.00 s)/1.56 cP=50.0.The term t₃ is the efflux time of the S-3 calibration oil used in thedetermination of the absolute viscosity of the formic acid as requiredin ASTM D789 (2015).

In some embodiments, the RV of the (precursor) polyamide has a lowerlimit of at least 2, e.g., at least 3, at least 4, or at least 5. Interms of upper limits, the polyamide has an RV of at 330 or less, 300 orless, 275 or less, 250 or less, 225 or less, 200 or less, 150 or less,100 or less, or 60 or less. In terms of ranges, the polyamide may havean RV of 2 to 330, e.g., from 2 to 300, from 2 to 275, from 2 to 250,from 2 to 225, from 2 to 200, 2 to 100, from 2 to 60, from 2 to 50, from2 to 40, from 10 to 40, or from 15 to 40 and any values in between.

In some embodiments, the RV of the nanofiber nonwoven product has alower limit of at least 2, e.g., at least 3, at least 4, or at least 5.In terms of upper limits, the nanofiber nonwoven product has an RV of at330 or less, 300 or less, 275 or less, 250 or less, 225 or less, 200 orless, 150 or less, 100 or less, or 60 or less. In terms of ranges, thenanofiber nonwoven product may have an RV of 2 to 330, e.g., from 2 to300, from 2 to 275, from 2 to 250, from 2 to 225, from 2 to 200, 2 to100, from 2 to 60, from 2 to 50, from 2 to 40, from 10 to 40, or from 15to 40, and any values in between.

The relationship between the RV of the (precursor) polyamide compositionand the RV of the nanofiber nonwoven product may vary. In some aspects,the RV of the nanofiber nonwoven product may be lower than the RV of thepolyamide composition. Reducing the RV conventionally has not been adesirable practice when spinning nylon 66. The inventors, however, havediscovered that, in the production of nanofibers, it is an advantage. Ithas been found that the use of lower RV polyamide nylons, e.g., lower RVnylon 66, in a melt spinning process has surprisingly been found toyield nanofiber filaments having unexpectedly small filament diameters.

The method by which the RV is lowered may vary widely. In some cases,process temperature may be raised to lower the RV. In some embodiments,however, the temperature raise may only slightly lower the RV sincetemperature affects the kinetics of the reaction, but not the reactionequilibrium constant. The inventors have discovered that, beneficially,the RV of the polyamide, e.g., the nylon 66, may be lowered bydepolymerizing the polymer with the addition of moisture. Up to 5%moisture, e.g., up to 4%, up to 3%, up to 2%, or up to 1%, may beincluded before the polyamide begins to hydrolyze. This techniqueprovides a surprising advantage over the conventional method of addingother polymers, e.g., polypropylene, to the polyamide (to reduce RV).

In some aspects, the RV may be raised, e.g., by lowering the temperatureand/or by reducing the moisture. Again, temperature has a relativelymodest effect on adjusting the RV, as compared to moisture content. Themoisture content may be reduced to as low as 1 ppm or greater, e.g., 5ppm or greater, 10 ppm or greater, 100 ppm or greater, 500 ppm orgreater, 1000 ppm or greater, or 2500 ppm or greater. Reduction ofmoisture content is also advantageous for decreasing TDI and ODI values,discussed further herein. Inclusion of a catalyst may affect thekinetics, but not the actual K value.

In some aspects, the RV of the nanofiber nonwoven product is at least20% less than the RV of the polyamide prior to spinning, e.g., at least25% less, at least 30% less, at least 35% less, at least 40% less, atleast 45% less, or at least 90% less.

In other aspects, the RV of the nanofiber nonwoven product is at least5% greater than the RV of the polyamide prior to spinning, e.g., atleast 10% greater, at least 15% greater, at least 20% greater, at least25% greater, at least 30% greater, or at least 35% greater.

In still further aspects, the RV of the polyamide and the RV of thenanofiber nonwoven product may be substantially the same, e.g., within5% of each other.

An additional embodiment of the present disclosure involves productionof a layer of filter media comprising polyamide nanofibers having anaverage fiber diameter of less than 1 micron, and having an RV of from 2to 330. In this alternate embodiment, preferable RV ranges include: 2 to330, e.g., from 2 to 300, from 2 to 275, from 2 to 250, from 2 to 225,from 2 to 200, 2 to 100, from 2 to 60, from 2 to 50, from 2 to 40, from10 to 40, or from 15 to 40. The nanofibers are subsequently converted tononwoven web. As the RV increases beyond about 20 to 30, operatingtemperature becomes a greater parameter to consider. At an RV above therange of about 20 to 30, the temperature must be carefully controlled soas the polymer melts for processing purposes. Methods or examples ofmelt techniques are described in U.S. Pat. No. 8,777,599 (incorporatedby reference herein), as well as heating and cooling sources which maybe used in the apparatuses to independently control the temperature ofthe fiber producing device. Non limiting examples include resistanceheaters, radiant heaters, cold gas or heated gas (air or nitrogen), orconductive, convective, or radiation heat transfer mechanisms.

Fiber Dimensions and Distributions

The fibers disclosed herein are nanofibers, e.g., fibers having anaverage fiber diameter of less than 1000 nm.

In the case of polyamides having an RV above 2 and less than 330, theaverage fiber diameter of the nanofibers in the fiber layer of thenonwoven may be less than 1 micron, e.g., less than 950 nanometers, lessthan 925 nanometers, less than 900 nanometers, less than 800 nanometers,less than 700 nanometers, less than 600 nanometers, or less than 500nanometers. In terms of lower limits, the average fiber diameter of thenanofibers in the fiber layer of the nonwoven may have an average fiberdiameter of at least 100 nanometers, at least 110 nanometers, at least115 nanometers, at least 120 nanometers, at least 125 nanometers, atleast 130 nanometers, or at least 150 nanometers. In terms of ranges,the average fiber diameter of the nanofibers in the fiber layer of thenonwoven may be from 100 to 1000 nanometers, e.g., from 110 to 950nanometers, from 115 to 925 nanometers, from 120 to 900 nanometers, from125 to 800 nanometers, from 125 to 700 nanometers, from 130 to 600nanometers, or from 150 to 500 nanometers. Such average fiber diametersdifferentiate the nanofibers formed by the spinning processes disclosedherein from nanofibers formed by electrospinning processes.Electrospinning processes typically have average fiber diameters of lessthan 100 nanometers, e.g., from 50 up to less than 100 nanometers.Without being bound by theory, it is believed that such small nanofiberdiameters may result in reduced strength of the fibers and increaseddifficulty in handling the nanofibers.

The use of the disclosed process and precursors leads to a specific andbeneficial distribution of fiber diameters. For example, less than 20%of the nanofibers may have a fiber diameter from greater than 700nanometers, e.g., less than 17.5%, less than 15%, less than 12.5%, orless than 10%. In terms of lower limits, at least 1% of the nanofibershave a fiber diameter of greater than 700 nanometers, e.g., at least 2%,at least 3%, at least 4%, or at least 5%. In terms of ranges, from 1 to20% of the nanofibers have a fiber diameter of greater than 700nanometers, e.g., from 2 to 17.5%, from 3 to 15%, from 4 to 12.5%, orfrom 5 to 10%. Such a distribution differentiates the nanofiber nonwovenproducts described herein from those formed by electrospinning (whichhave a smaller average diameter (50-100 nanometers) and a much narrowerdistribution) and from those formed by non-nanofiber melt spinning(which have a much greater distribution). For example, a non-nanofibercentrifugally spun nonwoven is disclosed in WO 2017/214085 and reportsfiber diameters of 2.08 to 4.4 microns but with a very broaddistribution reported in FIG. 10A of WO 2017/214085.

In an embodiment, advantages are envisioned having two related polymerswith different RV values (both less than 330 and having an average fiberdiameter less than 1 micron) blended for a desired property. Forexample, the melting point of the polyamide may be increased, the RVadjusted, or other properties adjusted.

In some embodiments, the resultant nanofibers contain small amounts, ifany, of solvent. Accordingly, in some aspects, the resultant nanofibersare free of solvent. It is believed that the use of the melt spinningprocess advantageously reduces or eliminates the need for solvents. Thisreduction/elimination leads to beneficial effects such as environmentalfriendliness and reduced costs. Fibers formed via solution spinningprocesses, which are entirely different from melt spinning processesdescribed herein, require such solvents. In some embodiments, thenanofibers comprise less than 1 wt. % solvent, less than 5000 ppm, lessthan 2500 ppm, less than 2000 ppm, less than 1500 ppm, less than 1000ppm, less than 500 ppm, less than 400 ppm, less than 300 ppm, less than200 ppm, less than 100 ppm, or less than a detectable amount of solvent.Solvents may vary depending on the components of the polyamide but mayinclude formic acid, sulfuric acid, toluene, benzene, chlorobenzene,xylene/chlorohexanone, decalin, paraffin oil, ortho dichlorobenzene, andother known solvents. In terms of ranges, when small amounts of solventare included, the resultant nanofibers may have at least 1 ppm, at least5 ppm, at least 10 ppm, at least 15 ppm, or at least 20 ppm solvent. Insome aspects, non-volatile solvents, such as formic acid, may remain inthe product and may require an additional extraction step. Such anadditional extraction step may add to production costs.

In some cases, the nanofiber may be made of a polyamide material thatoptionally includes an additive. Examples of suitable additives includeoils (such as finishing oils, e.g., silicone oils), waxes, solvents(including formic acid as described herein), lubricants (e.g., paraffinoils, amide waxes, and stearates), stabilizers (e.g., photostabilizers,UV stabilizers, etc.), delusterants, antioxidants, colorants, pigments,and dyes. The additives may be present in a total amount of up to 49 wt.% of the nanofiber nonwoven product, e.g., up to 40 wt. %, up to 30 wt.%, up to 20 wt. %, up to 10 wt. %, up to 5 wt. %, up to 3 wt. %, or upto 1 wt. %. In terms of lower limits, the additives may be present inthe nanofiber product in an amount of at least 0.01 wt. %, e.g., atleast 0.05 wt. %, at least 0.1 wt. %, at least 0.25 wt. %, or at least0.5 wt. %. In terms of ranges, the additives may be present in thenanofiber product in an amount from 0.01 to 49 wt. %, e.g., from 0.05 to40 wt. %, from 0.1 to 30 wt. %, from 0.25 to 20 wt. %, from 0.5 to 10wt. %, from 0.5 to 5 wt. %, or from 0.5 to 1 wt. %. In some aspects,monomers and/or polymers may be included as additives. For example,nylon 61 and/or nylon 6T may be added as an additive.

Antioxidants suitable for use in conjunction with the nanofiber nonwovenproduct described herein may, in some embodiments, include, but are notlimited to, anthocyanin, ascorbic acid, glutathione, lipoic acid, uricacid, resveratrol, flavonoids, carotenes (e.g., beta-carotene),carotenoids, tocopherols (e.g., alpha-tocopherol, beta-tocopherol,gamma-tocopherol, and delta-tocopherol), tocotrienols, ubiquinol, gallicacids, melatonin, secondary aromatic amines, benzofuranones, hinderedphenols, polyphenols, hindered amines, organophosphorus compounds,thioesters, benzoates, lactones, hydroxylamines, and the like, and anycombination thereof. In some embodiments, the antioxidant may beselected from the group consisting of stearyl3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate,bis(2,4-dicumylphenyl)pentaerythritol diphosphite,tris(2,4-di-tert-butylphenyl)phosphite, bisphenol A propoxylatediglycidyl ether, 9,10-dihydroxy-9-oxa-10-phosphaphenanthrene-10-oxideand mixtures thereof.

Colorants, pigments, and dyes suitable for use in conjunction with thenanofiber nonwoven product described herein may, in some embodiments,include, but are not limited to, plant dyes, vegetable dyes, titaniumdioxide (which may also act as a delusterant), carbon black, charcoal,silicon dioxide, tartrazine, E102, phthalocyanine blue, phthalocyaninegreen, quinacridones, perylene tetracarboxylic acid di-imides,dioxazines, perinones disazo pigments, anthraquinone pigments, metalpowders, iron oxide, ultramarine, nickel titanate, benzimidazoloneorange gl, solvent orange 60, orange dyes, calcium carbonate, kaolinclay, aluminum hydroxide, barium sulfate, zinc oxide, aluminum oxide,CARTASOL® dyes (cationic dyes, available from Clariant Services) inliquid and/or granular form (e.g., CARTASOL Brilliant Yellow K-6Gliquid, CARTASOL Yellow K-4GL liquid, CARTASOL Yellow K-GL liquid,CARTASOL Orange K-3GL liquid, CARTASOL Scarlet K-2GL liquid, CARTASOLRed K-3BN liquid, CARTASOL Blue K-5R liquid, CARTASOL Blue K-RL liquid,CARTASOL Turquoise K-RL liquid/granules, CARTASOL Brown K-BL liquid),FASTUSOL® dyes (an auxochrome, available from BASF) (e.g., Yellow 3GL,Fastusol C Blue 74L), and the like, any derivative thereof, and anycombination thereof. In some embodiments, solvent dyes may be employed.

Method of Forming the Nanofibers

As described herein, the nanofiber nonwoven product is formed byspinning to form a spun product. “Island-in-the-sea” refers to fibersforming by extruding at least two polymer components from one spinningdie, also referred to as conjugate spinning. As used herein, spinningspecifically excludes solution spinning and electrospinning.

In some aspects, the polyamide nanofiber is melt blown. Melt blowing isadvantageously less expensive than electrospinning. Melt blowing is aprocess type developed for the formation of nanofibers and nonwovenwebs; the nanofibers are formed by extruding a molten thermoplasticpolymeric material, or polyamide, through a plurality of small holes.The resulting molten threads or filaments pass into converging highvelocity gas streams which attenuate or draw the filaments of moltenpolyamide to reduce their diameters. Thereafter, the melt blownnanofibers are carried by the high velocity gas stream and deposited ona collecting surface, or forming wire, to form a nonwoven web ofrandomly disbursed melt blown nanofibers. The formation of nanofibersand nonwoven webs by melt blowing is well known in the art. See, by wayof example, U.S. Pat. Nos. 3,016,599; 3,704,198; 3,755,527; 3,849,241;3,978,185; 4,100,324; 4,118,531; and 4,663,220.

As is well known, electrospinning has many fabrication parameters thatmay limit spinning certain materials. These parameters include:electrical charge of the spinning material and the spinning materialsolution; solution delivery (often a stream of material ejected from asyringe); charge at the jet; electrical discharge of the fibrousmembrane at the collector; external forces from the electrical field onthe spinning jet; density of expelled jet; and (high) voltage of theelectrodes and geometry of the collector. In contrast, theaforementioned nanofibers and products are advantageously formed withoutthe use of an applied electrical field as the primary expulsion force,as is required in an electrospinning process. Thus, the polyamide is notelectrically charged, nor are any components of the spinning process.Importantly, the dangerous high voltage necessary in electrospinningprocesses, is not required with the presently disclosedprocesses/products. In some embodiments, the process is anon-electrospin process and resultant product is a non-electrospunproduct that is produced via a non-electrospin process.

An embodiment of making the inventive nanofiber nonwovens is by way of2-phase spinning or melt blowing with propellant gas through a spinningchannel as is described generally in U.S. Pat. No. 8,668,854. Thisprocess includes two phase flow of polymer or polymer solution and apressurized propellant gas (typically air) to a thin, preferablyconverging channel. The channel is usually and preferably annular inconfiguration. It is believed that the polymer is sheared by gas flowwithin the thin, preferably converging channel, creating polymeric filmlayers on both sides of the channel. These polymeric film layers arefurther sheared into nanofibers by the propellant gas flow. Here again,a moving collector belt may be used and the basis weight of thenanofiber nonwoven is controlled by regulating the speed of the belt.The distance of the collector may also be used to control fineness ofthe nanofiber nonwoven. The process is better understood with referenceto FIG. 1.

Beneficially, the use of the aforementioned polyamide precursor in themelt spinning process provides for significant benefits in productionrate, e.g., at least 5% greater, at least 10% greater, at least 20%greater, at least 30% greater, at least 40% greater. The improvementsmay be observed as an improvement in area per hour versus a conventionalprocess, e.g., an electrospin process or a process that does not employthe features described herein. In some cases, the production increaseover a consistent period of time is improved. For example, over a giventime period, e.g., one hour, of production, the disclosed processproduces at least 5% more product than a conventional process or anelectrospin process, e.g., at least 10% more, at least 20% more, atleast 30% more, or at least 40% more.

FIG. 1 illustrates schematically operation of a system for spinning ananofiber nonwoven including a polyamide feed assembly 110, an air feed1210 a spinning cylinder 130, a collector belt 140 and a take up reel150. During operation, polyamide melt or solution is fed to spinningcylinder 130 where it flows through a thin channel in the cylinder withhigh pressure air, shearing the polyamide into nanofibers. Details areprovided in the aforementioned U.S. Pat. No. 8,668,854. The throughputrate and basis weight is controlled by the speed of the belt.Optionally, functional additives such as charcoals, copper or the likecan be added with the air feed, if so desired.

In an alternate construction of the spinneret used in the system of FIG.1, particulate material may be added with a separate inlet as is seen inU.S. Pat. No. 8,808,594.

Still yet another methodology which may be employed is melt blowing thepolyamide nanofiber webs disclosed herein (FIG. 2). Melt blowinginvolves extruding the polyamide into a relatively high velocity,typically hot, gas stream. To produce suitable nanofibers, carefulselection of the orifice and capillary geometry as well as thetemperature is required as is seen in: Hassan et al., J Membrane Sci.,427, 336-344, 2013 and Ellison et al., Polymer, 48 (11), 3306-3316,2007, and, International Nonwoven Journal, Summer 2003, pg 21-28.

U.S. Pat. No. 7,300,272 discloses a fiber extrusion pack for extrudingmolten material to form an array of nanofibers that includes a number ofsplit distribution plates arranged in a stack such that each splitdistribution plate forms a layer within the fiber extrusion pack, andfeatures on the split distribution plates form a distribution networkthat delivers the molten material to orifices in the fiber extrusionpack. Each of the split distribution plates includes a set of platesegments with a gap disposed between adjacent plate segments. Adjacentedges of the plate segments are shaped to form reservoirs along the gap,and sealing plugs are disposed in the reservoirs to prevent the moltenmaterial from leaking from the gaps. The sealing plugs can be formed bythe molten material that leaks into the gap and collects and solidifiesin the reservoirs or by placing a plugging material in the reservoirs atpack assembly. This pack can be used to make nanofibers with a meltblowing system described in the patents previously mentioned.

Additional Product Characteristics

The spinning processes described herein can form a polyamide nanofibernonwoven product having a relatively low oxidative degradation index(“ODI”) value. A lower ODI indicates less severe oxidative degradationduring manufacture. In some aspects, the ODI may range from 10 to 150ppm. ODI may be measured using gel permeation chromatography (GPC) witha fluorescence detector. The instrument is calibrated with a quinineexternal standard. 0.1 grams of nylon is dissolved in 10 mL of 90%formic acid. The solution is then analyzed by GPC with the fluorescencedetector. The detector wavelengths for ODI are 340 nm for excitation and415 nm for emission. In terms of upper limits, the ODI of the polyamidenanofiber nonwoven may be 200 ppm or less, e.g., 180 ppm or less, 150ppm or less, 125 ppm or less, 100 ppm or less, 75 ppm or less, 60 ppm orless, or 50 ppm or less. In terms of the lower limits, the ODI of thepolyamide nanofiber nonwoven may be 1 ppm or greater, 5 ppm or greater,10 ppm or greater, 15 ppm or greater, 20 ppm or greater, or 25 ppm orgreater. In terms of ranges, the ODI of the polyamide nanofiber nonwovenmay be from 1 to 200 ppm, from 1 to 180 ppm, from 1 to 150 ppm, from 5to 125 ppm, from 10 to 100 ppm, from 1 to 75 ppm, from 5 to 60 ppm, orfrom 5 to 50 ppm.

Additionally, the spinning processes as described herein can result in arelatively low thermal degradation index (“TDI”). A lower TDI indicatesa less severe thermal history of the polyamide during manufacture. TDIis measured the same as ODI, except that the detector wavelengths forTDI are 300 nm for excitation and 338 nm for emission. In terms of upperlimits, the TDI of the polyamide nanofiber nonwoven may be 4000 ppm orless, e.g., 3500 ppm or less, 3100 ppm or less, 2500 ppm or less, 2000ppm or less, 1000 ppm or less, 750 ppm or less, or 700 ppm or less. Interms of the lower limits, the TDI of the polyamide nanofiber nonwovenmay be 20 ppm or greater, 100 ppm or greater, 125 ppm or greater, 150ppm or greater, 175 ppm or greater, 200 ppm or greater, or 210 ppm orgreater. In terms of ranges, the TDI of the polyamide nanofiber nonwovenmay be from 20 to 400 ppm, 100 to 4000 ppm, from 125 to 3500 ppm, from150 to 3100 ppm, from 175 to 2500 ppm, from 200 to 2000 ppm, from 210 to1000 ppm, from 200 to 750 ppm, or from 200 to 700 ppm.

TDI and ODI test methods are also disclosed in U.S. Pat. No. 5,411,710.Lower TDI and/or ODI values are beneficial because they indicate thatthe nanofiber nonwoven product is more durable than products havinggreater TDI and/or ODI. As explained above, TDI and ODI are measures ofdegradation and a product with greater degradation would not perform aswell. For example, such a product may have reduced dye uptake, lowerheat stability, lower life in a filtration application where the fibersare exposed to heat, pressure, oxygen, or any combination of these, andlower tenacity in industrial fiber applications.

One possible method that may be used in forming a nanofiber nonwovenproduct with a lower TDI and/or ODI would be to include additives asdescribed herein, especially antioxidants. Such antioxidants, althoughnot necessary in conventional processes, may be used to inhibitdegradation. An example of useful antioxidants include copper halidesand Nylostab® S-EED® available from Clariant.

The spinning methods as described herein may also result in a nanofibernonwoven product having an Air Permeability Value of less than 600CFM/ft², e.g., less than 590 CFM/ft², less than 580 CFM/ft², less than570 CFM/ft², less than 560 CFM/ft², or less than 550 CFM/ft². In termsof lower limits, the nanofiber nonwoven product may have an AirPermeability Value of at least 50 CFM/ft², at least 75 CFM/ft², at least100 CFM/ft², at least 125 CFM/ft², at least 150 CFM/ft², or at least 200CFM/ft². In terms of ranges, the nanofiber nonwoven product may have anAir Permeability Value from 50 to 600 CFM/ft², from 75 to 590 CFM/ft²,from 100 to 580 CFM/ft², from 125 to 570 CFM/ft², from 150 to 560CFM/ft², or from 200 to 550 CFM/ft².

The spinning methods as described herein may also result in a nanofibernonwoven product having a filtration efficiency, as measured by a TSI3160 automated filter tester from 1 to 99.999%, e.g., from 1 to 95%,from 1 to 90%, from 1.5 to 85%, or from 2 to 80%. The TSI 3160 AutomatedFilter Tester is used to test the efficiency of filter materials.Particle penetration and pressure drop are the two important parametersmeasured using this instrument. Efficiency is 100%—penetration. Achallenge solution with known particle size is used. The TSI 3160 isused to measure Hepa filters and uses a DOP solution. It combines anElectrostatic Classifier with dual Condensation Particle Counters (CPCs)to measure most penetrating particle size (MPPS) from 15 to 800 nm usingmonodisperse particles. And can test efficiencies up to 99.999999%.

Applications

The inventive nanofiber nonwovens are useful in a variety ofapplications due to their high temperature resistance, barrier,permeability properties, and, processability. The products may be usedin multilayer structures including laminates in many cases.

Thus, the products are used in air or liquid filtration in the followingsectors: transportation; industrial; commercial and residential.

The products are likewise suitable for barrier applications inbreathable fabrics, surgical nonwovens, baby care, adult care, apparel,composites, construction and acoustics. The compositions are useful forsound dampening in automotive, electronic and aircraft applicationswhich may require composites of different fiber sizes for bestperformance. At higher basis weights, the products are used inconnection with beverages, food packaging, transportation, chemicalprocessing and medical applications such as wound dressings or medicalimplants.

The unique characteristics of the nonwovens of the disclosure providefunctionality and benefits not seen in conventional products, forexample, the nonwovens of the disclosure can be used as packaging forsmoked meats.

EMBODIMENTS Embodiment 1

A nanofiber nonwoven product comprising polyamide nanofibers, whereinthe product has a relative viscosity from 2 to 330, and wherein thenanofibers have an average diameter from 100 to 1000 nanometers.

Embodiment 2

The nanofiber nonwoven product according to Embodiment 1, wherein themelt point of the product is 225° C. or greater.

Embodiment 3

The nanofiber nonwoven product according to Embodiment 1 or 2, whereinno more than 20% of the nanofibers have a diameter of greater than 700nanometers.

Embodiment 4

The nanofiber nonwoven product according to any of Embodiments 1-3,wherein the polyamide comprises nylon 66 or nylon 6/66.

Embodiment 5

The nanofiber nonwoven product according to any of Embodiments 1-4,wherein the polyamide is a high temperature nylon.

Embodiment 6

The nanofiber nonwoven product according to any of Embodiments 1-5,wherein the polyamide comprises N6, N66, N6T/66, N612, N6/66, N6I/66,N66/6I/6T, N11, and/or N12, wherein “N” means Nylon.

Embodiment 7

The nanofiber nonwoven product according to any of Embodiments 1-6,wherein the product has an Air Permeability Value of less than 600CFM/ft².

Embodiment 8

The nanofiber nonwoven product according to any of Embodiments 1-7,wherein the product has a basis weight of 150 GSM or less.

Embodiment 9

The nanofiber nonwoven product according to any of Embodiments 1-8,wherein the product has a TDI of at least 20 ppm.

Embodiment 10

The nanofiber nonwoven product according to any of Embodiments 1-9,wherein the product has an ODI of at least 1 ppm.

Embodiment 11

The nanofiber nonwoven product according to any of Embodiments 1-10,wherein the product is free of solvent.

Embodiment 12

The nanofiber nonwoven product according to any of Embodiments 1-10,wherein the product comprises less than 5000 ppm solvent.

Embodiment 13

The nanofiber nonwoven product according to any of Embodiments 1-12,wherein at least 1% of the nanofibers have a diameter of at least 700nm.

Embodiment 14

The nanofiber nonwoven product according to any of Embodiments 1-13,wherein the polyamide precursor had a moisture content of at least 5ppm.

Embodiment 15

The nanofiber nonwoven product according to any of Embodiments 1-14,wherein the polyamide precursor had a moisture content of no more than 3wt. %.

Embodiment 16

The nanofiber nonwoven product according to any of Embodiments 1-14,wherein the polyamide precursor had an RV from 2 to 330.

Embodiment 17

The nanofiber nonwoven product according to Embodiment 16, wherein theRV of the nanofiber nonwoven product is reduced as compared to the RV ofthe polyamide precursor.

Embodiment 18

The nanofiber nonwoven product according to Embodiment 16, wherein theRV of the nanofiber nonwoven product stays the same or is increased ascompared to the RV of the polyamide precursor.

Embodiment 19

A nanofiber nonwoven product comprising a polyamide which is spun intonanofibers with an average diameter from 100 to 1000 nanometers andformed into said nonwoven product, wherein the polyamide has a relativeviscosity from 2 to 330.

Embodiment 20

The nanofiber nonwoven product according to Embodiment 19, wherein themelt point of the product is 225° C. or greater.

Embodiment 21

The nanofiber nonwoven product according to Embodiment 19 or 20, whereinno more than 20% of the nanofibers have a diameter of greater than 700nanometers.

Embodiment 22

The nanofiber nonwoven product according to any of Embodiments 19-21,wherein the polyamide comprises nylon 66 or nylon 6/66.

Embodiment 23

The nanofiber nonwoven product according to any of Embodiments 19-22,wherein the polyamide is a high temperature nylon.

Embodiment 24

The nanofiber nonwoven product according to an of Embodiments 19-23,wherein the polyamide comprises N6, N66, N6T/66, N612, N6/66, N6I/66,N66/6I/6T, N11, and/or N12, wherein “N” means Nylon.

Embodiment 25

The nanofiber nonwoven product according to any of Embodiments 19-24,wherein the product has an Air Permeability Value of less than 600CFM/ft².

Embodiment 26

The nanofiber nonwoven product according to any of Embodiments 19-25,wherein the product has a basis weight of 150 GSM or less.

Embodiment 27

The nanofiber nonwoven product according to any of Embodiments 19-26,wherein the product has a TDI of at least 20 ppm.

Embodiment 28

The nanofiber nonwoven product according to any of Embodiments 19-27,wherein the product has an ODI of at least 1 ppm.

Embodiment 29

The nanofiber nonwoven product according to any of Embodiments 19-28,wherein the product is free of solvent.

Embodiment 30

The nanofiber nonwoven product according to any of Embodiments 19-29,wherein the product comprises less than 5000 ppm solvent.

Embodiment 31

The nanofiber nonwoven product according to any of Embodiments 10-30,wherein at least 1% of the nanofibers have a diameter of at least 700nm.

Embodiment 32

The nanofiber nonwoven product according to any of Embodiments 19-31,wherein the polyamide has a moisture content of at least 5 ppm.

Embodiment 33

The nanofiber nonwoven product according to any of Embodiments 19-32wherein the polyamide has a moisture content of no more than 3 wt. %.

Embodiment 34

The nanofiber nonwoven product according to any of Embodiments 19-33wherein the product has an RV from 2 to 330.

Embodiment 35

The nanofiber nonwoven product according to Embodiment 34, wherein theRV of the nanofiber nonwoven product is reduced as compared to the RV ofthe polyamide precursor.

Embodiment 36

The nanofiber nonwoven product according to Embodiment 34, wherein theRV of the nanofiber nonwoven product stays the same or is increased ascompared to the RV of the polyamide precursor.

Embodiment 37

A method of making a nanofiber nonwoven product, the method comprising:(a) providing a polyamide composition, wherein the polyamide has arelative viscosity from 2 to 330; (b) spinning the polyamide compositioninto a plurality of nanofibers having an average fiber diameter from 100to 1000 nanometers; and (c) forming the nanofibers into the nanofibernonwoven product, wherein the polyamide nanofiber layer has an averagenanofiber diameter from 100 to 1000 nanometers and a relative viscosityfrom 2 to 330.

Embodiment 38

The method of making the nanofiber nonwoven product according toEmbodiment 37, wherein the polyamide composition is melt spun by way ofmelt-blowing through a die into a high velocity gaseous stream.

Embodiment 39

The method of making the nanofiber nonwoven product according toEmbodiment 37 or 38, wherein the polyamide composition is melt-spun by2-phase propellant-gas spinning, including extruding the polyamidecomposition in liquid form with pressurized gas through a fiber-formingchannel.

Embodiment 40

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-39, wherein the nanofiber nonwoven product is formed bycollecting the nanofibers on a moving belt.

Embodiment 41

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-40, wherein the polyamide nanofiber layer has a basisweight of 150 GSM or less.

Embodiment 42

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-41, wherein the relative viscosity of the polyamide inthe nanofiber nonwoven product is reduced as compared to the polyamidecomposition prior to spinning and forming the product.

Embodiment 43

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-41, wherein the relative viscosity of the polyamide inthe nanofiber nonwoven product is the same or increased as compared tothe polyamide composition prior to spinning and forming the product.

Embodiment 44

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-43, wherein the production rate of the method of steps(a)-(c) is at least 5% greater than an electrospinning or solutionspinning production rate.

Embodiment 45

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-44, wherein the melt point of the product is 225° C. orgreater.

Embodiment 46

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-45, wherein no more than 20% of the nanofibers have adiameter of greater than 700 nanometers.

Embodiment 47

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-46, wherein the polyamide comprises nylon 66 or nylon6/66.

Embodiment 48

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-47, wherein the polyamide is a high temperature nylon.

Embodiment 49

The method of making the nanofiber nonwoven product according to any ofEmbodiments, 37-48 wherein the polyamide comprises N6, N66, N6T/66,N612, N6/66, N6I/66, N66/6I/6T, N11, and/or N12, wherein “N” meansNylon.

Embodiment 50

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-49, wherein the product has an Air Permeability Value ofless than 600 CFM/ft².

Embodiment 51

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-50, wherein the product has a basis weight of 150 GSM orless.

Embodiment 52

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-51, wherein the product has a TDI of at least 20 ppm.

Embodiment 53

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-52, wherein the product has an ODI of at least 1 ppm.

Embodiment 54

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-53, wherein the product is free of solvent.

Embodiment 55

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-54, wherein the product comprises less than 5000 ppmsolvent.

Embodiment 56

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-55, wherein at least 1% of the nanofibers have a diameterof at least 700 nm.

Embodiment 57

The method of making the nanofiber nonwoven product according to any ofEmbodiments, 37-56 wherein the polyamide precursor had a moisturecontent of at least 5 ppm.

Embodiment 58

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-57, wherein the polyamide precursor had a moisturecontent of no more than 3 wt. %.

Embodiment 59

The method of making the nanofiber nonwoven product according to any ofEmbodiments 37-57, wherein the polyamide precursor had a moisturecontent from 10 ppm to 5 wt. %.

Embodiment 60

A nanofiber nonwoven product comprising a polyamide composition formedinto said nonwoven product, wherein the product has at least one of thefollowing: (i) a TDI from 20 to 4000 ppm, (ii) an ODI from 1 to 200 ppm,(iii) an average nanofiber diameter from 100 to 1000 nanometers, (iv) apolyamide comprising nylon 6,6, and (v) a polyamide composition RV from2 to 330.

Embodiment 61

A nanofiber nonwoven product comprising a nylon 66 polyamide which ismelt spun into nanofibers and formed into said nonwoven product, whereinthe product has a TDI of at least 20 ppm and an ODI of at least 1 ppm.

Embodiment 62

A nanofiber nonwoven product comprising a nylon 66 polyamide which ismelt spun into nanofibers and formed into said nonwoven product, whereinno more than 20% of the nanofibers have a diameter of greater than 700nanometers.

Embodiment 63

The nanofiber nonwoven product according to any of Embodiments 60-62,wherein the melt point of the product is 225° C. or greater.

Embodiment 64

The nanofiber nonwoven product according to any of Embodiments 60-61 and63, wherein no more than 20% of the nanofibers have a diameter ofgreater than 700 nanometers.

Embodiment 65

The nanofiber nonwoven product according to any of Embodiments 60-64,wherein the product has an Air Permeability Value of less than 600CFM/ft2.

Embodiment 66

The nanofiber nonwoven product according to any of Embodiments 60-65,wherein the product has a basis weight of 150 GSM or less.

Embodiment 67

The nanofiber nonwoven product according to any of Embodiments 62-66,wherein the product has a TDI of at least 20 ppm.

Embodiment 68

The nanofiber nonwoven product according to any of Embodiments 62-67,wherein the product has an ODI of at least 1 ppm.

Embodiment 69

The nanofiber nonwoven product according to any of Embodiments 60-68,wherein the product is free of solvent.

Embodiment 70

The nanofiber nonwoven product according to any of Embodiments 60-68,wherein the product comprises less than 5000 ppm solvent.

Embodiment 71

The nanofiber nonwoven product according to any of Embodiments 60-70,wherein the polyamide has a moisture content of at least 5 ppm.

Embodiment 72

The nanofiber nonwoven product according to any of Embodiments 60-71,wherein the polyamide has a moisture content of no more than 3 wt. %.

Embodiment 73

The nanofiber nonwoven product according to any of Embodiments 60-72,wherein the product has an RV from 2 to 330.

Embodiment 74

The nanofiber nonwoven product according to Embodiment 73, wherein theRV of the nanofiber nonwoven product is reduced as compared to the RV ofthe polyamide precursor.

Embodiment 75

The nanofiber nonwoven product according to Embodiment 73, wherein theRV of the nanofiber nonwoven product stays the same or is increased ascompared to the RV of the polyamide precursor

The present disclosure is further understood by the followingnon-limiting examples.

EXAMPLES Example 1

Utilizing the (melt) spin procedures and apparatus as described in U.S.Pat. No. 8,668,854 (shown generally in FIG. 1), Nylon 66 polyamide wasspun onto a moving drum to produce nonwoven webs. The process employedan extruder with a high compression screw, operating at 20 RPM, with atemperature profile of 245° C., 255° C., 265° C., and 265° C. The(precursor) polyamide temperature was 252° C. and nitrogen was used asthe gas. Two nonwoven webs were produced (Samples 1 and 2), each havingdifferent basis weights. Sample 2 with the higher basis weight was madeby the same process, but the nanofibers were spun onto a scrim. In thisinstance, the scrim was merely used for adding integrity to theinventive nanofiber web. The polyamide had an RV of 7.3 (beforespinning). To ensure the constant viscosity of the low RV polyamidewould remain essentially constant, the polyamide was prepared using anexcess of about 5% adipic acid.

The nonwoven webs were characterized for average fiber diameter, basisweight, air permeability in accordance with the Hassan et al. articlenoted above. Water vapor transmission rate was also measured (g/m²/24hr) according to ASTM E96, Procedure B (2016).

The results are shown in Table 1, and the nonwoven mats are shown in thephotomicrographs of FIGS. 3 and 4. The nanofibers of the nonwoven matshad an average fiber diameter ranging from 470 nm to 680 nm (575 nmaverage).

TABLE 1 Example 1: Precursor Polyamide and Product Properties Basis AirFiber weight, permeability WVTR TDI ODI Final Sample PA RV diameter, nmGSM (CFM/ft²) g/m²/24 hr (ppm) (ppm) RV 1 7.3 680 68 182.8 1140 56 12 102 7.3 470 118 182.8 1056 48 8 9.9

As shown in Table 1, the use of the processes disclosed herein providedfor a melt spun nanofiber nonwoven web, the nanofibers of which had afiber diameter averaging 570 for the RV of 7.3. Air Permeability wasabout 182.8 CFM/ft2, while water vapor transmission rate averaged about1100 g/sq meter/24 hrs. Such fiber diameters and performancecharacteristics have not been achieved using conventional polyamideprecursors and/or processes. Without being bound by theory, it isbelieved that the use of the low RV polyamide composition (and/ornitrogen) was the main reason the TDI and ODI results were so low.

Example 2

Nylon 66 polyamide having an RV of 36 was melt spun and pumped to meltblown dies (utilizing the melt spin pack described in U.S. Pat. No.7,300,272 and illustrated in FIG. 5) to produce nonwoven nanofiber webs.In the various samples, the moisture levels of nylon 66 ranged fromabout 0.2% to about 1.0% (as shown in Table 2). An extruder with threezones was used, and the extruder operated at temperatures ranging from233° C. to 310° C. The die temperature ranged from 286° C. to 318° C.Heated air was used as the gas. The nanofibers were deposited onto a 10gsm thermally bonded, nylon spunbond scrim commercially available fromCerex Advanced Fabrics, Inc. under the trademark PBN-II®. Of course,other spunbond fabrics can be used, for example, a polyester spun bondfabric, a polypropylene spunbond fabric, a nylon melt blown fabric orother woven, knit, needlepunched, or other nonwoven fabrics. No solventsor adhesives were used during the melt spinning or deposition processes,and neither the polyamide or the resultant product contained solvent.

Various fabrics were made with webs of nanofibers. The properties andperformance characteristics of several specific samples are summarizedin Table 2.

TABLE 2 Example 2: Precursor Polyamide and Product Properties AverageNanofiber Mean Mean Fiber Basis layer Air pore size pore size FiltrationProduct diameter, weight, thickness permeability diameter pressureEfficiency Sample RV (microns) (gsm) (microns) (CFM/ft²) (microns) (PSI)(%) 3 27.45 0.374 3.0 N/A 187.20 10.123 0.653 24.69 4 25.17 0.595 21.2N/A 21.86 5.001 1.320 76.70 5 28.27 0.477 1.0 N/A 1002.00 84.123 0.812.71 6 22.93 0.5765 2.8 44.8 353.8 19.95 0.358 10.38 7 24.11 0.6008 7.360 757.2 7.85 0.919 40.68 8 23.91 0.4900 10.1 88 52.9 5.89 1.12 52.6 923.80 0.5950 13.2 101.5 75.72 7.185 1.235 66.00

As indicated in Table 2, the disclosed process surprisingly yieldsnanofibers and nonwoven mats having synergistic combinations offeatures. The nanofiber nonwoven mats were successfully made using theabove described process, in various basis weights with a wide range ofproperties. Process settings can be adjusted to provide nanofiberfabrics with a variety of properties as required for the application asillustrated in Table 2.

Example 3

A nylon 66 polyamide composition with an RV in the range of 34 to 37 wasused with the pack described in U.S. Pat. No. 7,300,272 to makenanofibers with an RV of about 16.8. This is a reduction in RV frompolyamide composition to fabric of about 17.2 to 20.2 RV units. Thepolyamide composition contained about 1% moisture by weight and was runon a small extruder with three zones ranging in temperature from 233 to310° C. A die temperature of about 308° C. was used. No solvents oradhesives were used during the melt spinning or deposition processes,and neither the polyamide or the resultant product contained solvents oradhesive.

Example 4

A nylon 66 polyamide composition with an RV in the range of 34 to 37with the pack described in U.S. Pat. No. 7,300,272 to make nanofiberswith an RV of about 19.7. This is a reduction in RV from polyamidecomposition to fabric of about 14.3 to 17.3 RV units. The polyamidecomposition contained 1% moisture by weight and was run on a smallextruder with three zones ranging in temperature from 233 to 310 C. Adie temperature of about 277° C. was used. No solvents or adhesives wereused during the melt spinning or deposition processes, and neither thepolyamide or the resultant product contained solvent or adhesive.

Example 5

A nylon 66 polyamide composition with an RV in the range of 34 to 37 wasused with 2% nylon 6 blended in. The pack described in U.S. Pat. No.7,300,272 was used to make nanofibers with an RV of about 17.1. This isa reduction in RV from polyamide composition to fabric of about 16.9 to19.9 RV units. The polyamide composition contained 1% moisture by weightand was run on a small extruder with three zones ranging in temperaturefrom 233 to 310° C. A die temperature of about 308° C. was used. Nosolvents or adhesives were used during the melt spinning or depositionprocesses, and neither the polyamide or the resultant product containedsolvent or adhesive.

Example 6

Seven polyamide compositions with varied RV's were provided as shownbelow in Table 3. The pack described in U.S. Pat. No. 7,300,272 was usedto make nanofibers with RV values as reported below. Samples were madeon a small extruder with a high residence time. Initially, Samples 10and 11 were made by feeding more than enough chips into the feed hopperof the extruder. In order to reduce the transition time between items,the extruder and die (or pack) were starved of polyamide compositionafter Sample 11. This example shows that a wide variety of nyloncopolymers can be used to make nylon nanofibers with fiber diameters inthe 0.53 to 0.68 micron range. Fiber diameters may be changed bychanging process parameters, polymer formulations, or polymer types(copolymers). Based on the way the samples were created, it is difficultto draw conclusions on the degradation indices of these fabrics otherthan Samples 10 and 11. Samples 10 and 11 indicate that the addition ofnylon 6 decreased the thermal degradation of the final nanofiber fabric.Comparing these samples to sample 16 also shows that adding nylon 6decreases the fiber diameter. Sample 13 shows that the RV was reducedfrom 303.1 to 33.3. This is a reduction of 269.8 units or an 89%reduction in RV.

TABLE 3 Example 6: Precursor Polyamide and Product Properties FiberPolyamide % Nylon Moisture Diameter Product ODI TDI Sample Components RV6, 6 (%) (microns) RV (ppm) (ppm) 10 Nylon 66/nylon 6 39.2 16 0.08100.531 29.7 75 798 11 Nylon 66/nylon 6 33.0 23 0.077 0.540 35.9 142 16912 Nylon 66 123.7 100 0.0351 0.588 39.1 182 1613 13 Nylon 66 303.1 1000.0177 0.638 33.3 208 1792 14 Nylon 66/nylon 6I 43.6 85 0.087 0.588 26.1172 2232 15 Nylon 66/nylon 6T 44.8 65 0.0422 N/A N/A 224 2383 16 Nylon66 36 100 0.022 0.684 15.2 1430 >4000

Example 7

A series of examples were run to test nanofiber samples for TDI and ODIas a function of die temperature. The same nylon 66 polyamidecomposition with an RV in the range of 34 to 37 that was used in example3 was run in each of these samples. These samples were made on aslightly larger extruder and a much larger die (pack) with a muchsmaller residence time than those in Table 3 with the same polyamidecomposition as that used to make sample 16. The die temperature, basisweight, and flake moisture were varied. Table 4 below shows theconditions and results. The results are also shown in the graphs inFIGS. 7 and 8. As shown in Table 4 below, changing process variablesdoes not dramatically change the ODI, illustrating a robust process foroxidative degradation. As shown in FIG. 8, as the meter pump speeddecreased, the ODI and TDI generally increased with the TDI increasingat a higher percentage than the ODI. When compared to Sample 16 in Table3, these samples show that the ODI and the TDI were lowered as thisequipment used to run the nanofiber nonwoven fabric was designed for alower residence time.

TABLE 4 Example 7: TDI and ODI Values Meter Die Pump Moisture BasisTemperature Speed TDI ODI Sample (%) Weight (° C.) (rpm) (ppm) (ppm) 160.2 13.20 299 5.37 745 66 17 0.2 18.40 292 5.37 608 47 18 0.3 3.7 2978.05 572 59 19 0.2 3.2 297 8.05 676 59 20 0.2 6.2 297 10.73 214 34 210.2 11 297 10.73 364 33 22 0.2 11 297 10.73 333 45 23 0.2 4.4 287 8.05398 33 24 0.2 6.1 286 10.73 354 26 25 0.2 8 286 8.05 492 39 26 0.3 4.1287 8.05 464 32 27 0.3 6 300 10.73 433 28 28 0.3 6 289 10.73 441 40

Example 8

Nylon 66 polyamide having an RV of 36 was melt spun and pumped to meltblown dies (utilizing the melt spin pack described in U.S. Pat. No.7,300,272 and illustrated in FIG. 5) to produce nonwoven nanofiber webs.The moisture level of nylon 66 was about 0.22%. An extruder with threezones was used, and the extruder operated at temperatures ranging from233° C. to 310° C. The die temperature was 295° C. Heated air was usedas the gas. The nanofibers were deposited onto a 10 gsm thermallybonded, nylon spunbond scrim commercially available from Cerex AdvancedFabrics, Inc. under the trademark PBN-II®. Of course, other spunbondfabrics can be used, for example, a polyester spun bond fabric, apolypropylene spunbond fabric, a nylon melt blown fabric or other woven,knit, needlepunched, or other nonwoven fabrics. No solvents or adhesiveswere used during the melt spinning or deposition processes, and neitherthe polyamide or the resultant product contained solvent or adhesive.The collector belt speed was set to make a fabric with a nylon 6,6nanofiber layer of 82 gsm basis weight. This fabric had an efficiency of97.9%, a pressure drop of 166.9 Pascals and a penetration of 2.1% asmeasured using the TSI 3160 previously discussed. This fabric had a meanflow pore diameter average of 5.8 microns with a range from 3.2 to 8microns. The air permeability of this fabric was 8.17 cfm/square foot.The thickness of the nanofiber layer was 625 microns.

Example 9 (Comparative)

Nylon 66 polyamide was melt spun into nonwoven samples 29 and 30utilizing a centrifugal spinning process where polymer fibers are formedby spinning the melt through a rotating spinneret. Description of thecentrifugal spinning process is seen in U.S. Pat. No. 8,658,067; WO2012/109251; U.S. Pat. No. 8,747,723 to Marshall et al., and U.S. Pat.No. 8,277,771. This process produced nylon nanofiber fibers withextraordinarily high TDI and ODI indices. These results are much greaterthan the samples in Example 7 made with the melt blown process describedherein.

TABLE 5 Nanofiber fabrics made with centrifugal spinning process SampleFabric RV TDI (ppm) ODI (ppm) 29 22 3759 1739 30 14.2 4378 3456

While the disclosure has been described in detail, modifications withinthe spirit and scope of the disclosure will be readily apparent to thoseof skill in the art. Such modifications are also to be considered aspart of the present disclosure. In view of the foregoing discussion,relevant knowledge in the art and references discussed above inconnection with the Background, the disclosures of which are allincorporated herein by reference, further description is deemedunnecessary. In addition, it should be understood from the foregoingdiscussion that aspects of the disclosure and portions of variousembodiments may be combined or interchanged either in whole or in part.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the disclosure. Finally, all patents, publications, andapplications referenced herein are incorporated by reference in theirentireties.

What is claimed is:
 1. A nanofiber nonwoven product comprising polyamidenanofibers and at least one additive, wherein the polyamide of thenanofibers comprises a nylon, nylon copolymer, nylon terpolymer, nylonblend, nylon derivative, or combinations thereof, wherein the at leastone additive comprises an oil, a wax, a solvent, a stabilizer, adelusterant, an antioxidant, a colorant, a pigment, a dye, orcombinations thereof wherein the polyamide of the nanofibers have arelative viscosity from 10 to 330, and wherein the nanofibers have anaverage diameter from 100 to 950 nanometers.
 2. The nanofiber nonwovenproduct according to claim 1, wherein the nanofiber nonwoven productcomprised staple nanofibers.
 3. The nanofiber nonwoven product accordingto claim 1, wherein the nanofiber nonwoven product comprises continuousnanofibers.
 4. The nanofiber nonwoven product according to claim 1,wherein the melt point of the nanofiber nonwoven product is between 223°C. and 390° C.
 5. The nanofiber nonwoven product according to claim 1,wherein the product has an Air Permeability Value of less than 600CFM/ft².
 6. The nanofiber nonwoven product according to claim 1, whereinthe polyamide nanofibers further comprise at least one of a polyolefin,a polyacetal, a polyester, a cellulose ether, a cellulose ester, apolyalkylene sulfide, a polyarylene oxide, a polysulfone, andcombinations thereof.
 7. The nanofiber nonwoven product according toclaim 1, wherein the polyamide nanofibers further comprise at least oneof polyethylene, a polybutylene terephthalate, a polypropylene, apoly(vinylchloride), a polymethylmethacrylate, a polystyrene, apoly(vinylidene fluoride), a poly(vinylidene chloride), a polyvinylalcohol, or combinations thereof.
 8. The nanofiber nonwoven productaccording to claim 1, wherein the polyamide nanofiber comprises Nylon 6,Nylon 66, Nylon 6,10, or combinations thereof.
 9. The nanofiber nonwovenproduct according to claim 1, wherein the polyamide nanofiber comprisesat least 0.1 wt. % Nylon 6, Nylon 66, Nylon 61, Nylon 6T, orcombinations thereof.
 10. The nanofiber nonwoven product according toclaim 1, wherein from 1 to 20% of the nanofibers have a fiber diameterof greater than 700 nanometers.
 11. The nanofiber nonwoven productaccording to claim 1, wherein all additives are present in a totalamount from 0.01 to 49 wt. %, based on the total weight of the nanofibernonwoven product.
 12. The nanofiber nonwoven product according to claim1, wherein the additive comprises a zinc compound.
 13. The nanofibernonwoven product according to claim 1, wherein the additive compriseszinc oxide.
 14. The nanofiber nonwoven product according to claim 1,wherein the additive comprises a copper compound.
 15. The nanofibernonwoven product according to claim 1, wherein the nanofiber nonwovenproduct has a TDI from 20 to 400 ppm and an ODI from 1 to 200 ppm. 16.The nanofiber nonwoven product according to claim 1, wherein thenanofiber nonwoven product comprises less than 5000 ppm solvent.
 17. Thenanofiber nonwoven product according to claim 1, wherein the nanofibernonwoven product has a filtration efficiency from 1 to 99.999%.
 18. Ananofiber nonwoven product comprising polyamide nanofibers, wherein thepolyamide of the nanofibers comprises a non-nylon polyamide, wherein thepolyamide of the nanofibers have a relative viscosity from 4 to 330, andwherein the nanofibers have an average diameter from 100 to 950nanometers.